Compensator



Nov. 24, 1964 w. J. FANT ETAL 3,157,969

COMPENSATOR Filed Dec. 4, 1962 4 Sheets-Sheet 1 1 I I m O /9 25 UnitedStates Patent 3,157,?69 1 CQMF'ENSATUR William J. Fant and Adrain VanWylr, Grand Rapids, Mich, assignors to Gaihneyer dz Livingston Company,Grand Rapids, Mich, a corgoration of Michigan Filed Dec. 4 1962, er. No.242,209

6 (ilaims. {CL 51-465) This invention relates to a grinder, and moreparticularly to a wheel compensating mechanism in combination with aprecision grinder.

Modern technology often demands extremely accurate tolerances onfinished metal parts. The finishing operation on such parts is usuallymade with a precision grinder. However, when the grinder feed is pre-setto re move an exact total amount of stock from the workpiece, it iscommon knowledge that, due to appreciable Wheel Wear which varies withthe wheel composition, rate of feed, and workpiece characteristics,among other things, the actual thickness of stock removed is less thanthe pre-set desired value. The discrepancy or difference is equal to theamount of wheel wear occurring during the operation. This dilference canbe extremely important in the manufacture of precision parts finished to0.0001 inch, for example. The human operator cannot accurately andconveniently measure the amount of discrepancy and manually adjust thegrinder each time to remove it.

Another complicating factor involves the fact that the grinding wheelsurface ordinarily becomes untrue after, several passes, due to unevenwear of the wheel and the embedding of workpiece particles into thewheel. Therefore, as is well-known, the wheel surface should be dressedbefore the final finishing pass or passes are made. However, the wheelloss occurring with the dressing operation makes the task of removingthe exact amount of stock on the workpiece even more diificult since thewheel must first'be moved toward the workpiece the amount equal to thedressing loss, i.e. it must be rought into extremely light sparkingcontact, and then it must be advanced an amount exactly equal to thewheel wear. This may involve plus or minus 0.0001 inch. Consequently, todo this with extreme accuracy is usually impossible.

It is therefore an object of this invention to provide a grinder thatremoves the exact predetermined amount of stock from the workpiece toobtain extremely accuratetolerances, without any discrepancy between theamount ofstock pre-set to be removed, and that actually removed. This isachieved irrespective of the type or composition of the wheel, theamount of wheel wear, the hardness of the stock, the thickness of stockto be removed, the number of one or more wheel dressing steps before thefinal pass, or the amount of wheel removed by dressing. The lack of anydiscrepancy between the pre-set desired amount of stock removal and theactual amount of stock removal is achieved every time and automaticallyby automatic compensation of the wheel feed when dressing the wheel.

It is another object of this invention to provide a compensated grinderin which the wheel feed is compensated simultaneously and automaticallywith the feed of the dressingutool toward the wheel. The compensation,just prior to the final finishing pass or passes on the workpiece,adjusts the wheel an amount exactly equal to the feed of the dressingtool from a pre-established reference, and accounts inherently both forwheel loss during dressing and for wheelwear during previous grindingpasses. The compensation for these factors is exactly accurateregardless of the amount of wheel wear, the amount of wheel loss bydressing, the number of dressing passes, the type of wheel, the stockcharacteristics, or other factors.

. tional fashion.

Ice

The apparatus repeatedly performs this compensation functionindependently of the conventional wheel feed, and without disrupting oradversely affecting the conventional wheel feed mechanism, whethermanual or automatic.

These and other objects of this invention will be apparent upon studyingthe following specification in conjunction with the drawings, in which:

FIG. 1 is a perspective front view of a grinder embodying the novelcompensation apparatus;

FIG. 2 is a fragmentary, side elevational, sectional view of the wheeldressing control apparatus of the novel compensating unit;

FIG. 3 is a front elevational, fragmentary, partially sectional view ofthe apparatus in FIG. 2;

FIG. 4 is a plan, partially sectioned, fragmentary View of the spindleadjustment mechanism of the compensating apparatus;

FIG. 5 is a side elevational, sectional view of the apparatus in FIG. 4;

FIG. 6 is a sectional view through a portion of the apparatus in FIG. 2showing the switching control mechanism for the wheel dressing andcompensating apparatus in FIGS. 2 and 4;

FIG. 7 is a diagrammatic representation of the dressing tool, grindingwheel and workpiece at the beginning of the operation; and

FIG. 8 is a diagrammatic elevational representation of the apparatus inFIG. 7 illustrating the grinding, dressing, and compensating steps inthe operation.

Basically, the inventive grinder comprises a main frame includinga'workpiece bed support and a slidable spindle and wheel housing inwhich are rotatably mounted a spindle and grinding wheel, a dressingtool mounted to the spindle housing and adapted to normally movetherewith, but also including drive means operated by a stepping motorto adjust the tool with respect to the housing and towards or away fromthe wheel, wheel feed drive means for the adjustable spindle housing andwheel including a second stepping motor independent of the mainwheelfeed motor drive mechanism. Both stepping motors are electricallyconnected to a switching means so that switch actuation simultaneouslycauses dressing tool feed towards the wheel and an equal amount ofmovement of the spindle housing and wheel towards the workpiece, tocompensate for all wheel loss due to dressing and for wheel wear. Thespindle compensating means includes the stepping motor which drives aworm gear engaged with a gear collar around a screw shaftwhichvertically adjusts the spindle housing. The main wheel feed motor alsooperates this same screw shaft inan independent manner. The dressingtool also operates from a screw shaft rotated by an eletcrical steppingmotor through a worm gear.

Referring now specifically to the drawings, the grinding apparatus 10includes a conventional base 12, upright back 14, table or workpiece bedsupport 16 for holding a workpiece, and a grinding wheel assembly 18inciuding a spindle and wheel housing assembly vertically slidablyadjustable in ways with respect to the bed 16, and including an abrasivewheel 20 and protective shield 22. The bed 15 is adapted to reciprocatelongitudinally by conventional mechanism (not shown). It

may be manually moved longitudinally/by a crank 24 operating-a pinionand gear rack mechanism in conven- The bed may be laterally shifted backand forth by manual crank 25 and a conventional connected gear and rackassembly for cross feed.

The grinding wheel may be fed toward workpiece supported on bed 6,either manually or automatically in increments according to conventionalmethods. 7 For purposes of illustration, the wheel 44 in FIG. 1 canrepresent either a manually rotatable wheel or crank for manuallyfeeding the grinding wheel through a worm 52 (FIG. 5) mounted on a shaftoperated by the hand wheel 44, or may be a dial wheel for setting andindicating the incremental feed of the grinding wheel when worm gear 52is driven by an electrical motor 50. The incremental feed can beregulated using a control panel 42 of switch actuators. The tablereciprocation is controlled using auxiliary control means 36 to regulateits speed of traverse, means 38 to regulate stroke length, and means 39for stopping and starting. Bed reciprocation may be reversed by plunger40.

The worm 52, whether operated manually or automatically, rotates gearcollar 54 rotatably keyed with key 59 to screw shaft 56. This screwshaft 56 supports the spindle housing 58 (FIG. 2) on the lower end ofthe shaft and is rotatable with respect thereto on thrust bearings 66 orthe equivalent. Thus, rotation of motor 50 causes rotation of worm gear52, of gear 54, and of shaft 56. The shaft turns inside gear collar 80which has internal screw threads. Since collar 80 will not rotatetherewith (for reasons explained hereinafter), screw shaft 56 moves upor down to raise or lower the spindle housing 58 on the lower end of theshaft.

Mounted in spindle housing 53 on bearings 70 is a conventional spindle68. Affixed to the outer end of spindle 68 by nut 72 is a conventionalgrinding wheel 21) inside protective wheel housing 23 including a frontshield 22. Thus, raising and lowering of the spindle housing and wheelhousing and thereby also raises and lowers spindle 68 and wheel 20. 7

Gear collar 80 threadably engaged with screw shaft 56 by screw threadson its interior, has gear teeth 32 on its exterior. Collar 80 isrotatable on screw 56, and is supported on bearings 84 within theupright back 14 of the grinder. A cylindrical casing 86 covers the upperend of the screw shaft above this collar assembly. Gear teeth 82 engagea second worm 90 (FIG. 4) supported on suitable bearings 92 and 94 andoperably connected through drive connection 96 to an electrical steppingmotor 98 resembling a rotary solenoid. This stepping motor has a slowbasic shaft speed with almost negligible over-shoot. Each rotation ofthe motor may include several precise incremental moves such as 160 or200. It has a high torque, with each step being made instantly withoutflip or chatter. A typical motor is the SLO-SYN synchronous motorproduced by the Superior Electric Company, Bristol, Connecticut.Rotation of motor 98 in an incremental fashion rotates drive connection96 and worm gear 90 tiny amounts to thus rotate collar 86 slightly onbearings 84. Screw 56 does not rotate with the collar 80 since theconnection of worm 52 and gear 54 keyed to shaft 56 prevents'itsrotation. Therefore, rotation of collar 80 causes vertical movement ofshaft 56 without rotation. This raises or lowers the spindle housingsupported on the shaft to raise or lower grinding wheel with respect tothe workpiece 190 on the bed 16.

It will now be seen that the engagement of worm 90 with gear collar 80prevents rotation of gear collar 80 when shaft 56 is rotated by worm 52and gear 54.

Referring to FIG. 2 mounted above the wheel housing 23 and wheel 20 is adressing tool assembly 166, including a plunger 102 fitting through anopening in a slide'plate 104, and having a dressing tool 106 r'ernovablymounted in the lower end thereof. The tool includes a diamond tip 107.The cylindrical support plunger 1&2 is adapted to reciprocatetransversely across the surface of the wheel 20 between the positionillustrated in solid lines in FIG. 2 to that illustrated in dottedlines. It moves back and forth with the bearing slide plate 154 ascontrol ed by a conventional hydraulic reciprocating apparatus 108 cotrolled by a manual actuator 110. Thus, the dressing tool can move backand forth across the wheel to dress the wheel in a conventional fashion.plunger or post 102 has a hollow upper end and is The diamond supportthreadably engaged (FIG. 3) with screw shaft 112. To manually adjust thetool, a setting dial 114 is supplied. Since, however, it is afiixed tothe upper end of the screw shaft, and the screw shaft is locked intoengagement with the wheel feed, the dial 114 can only be rotatedmanually when the relationship is unlocked temporarily to allow the dialto manually cause vertical movement of plunger 102. Rotation of theplunger is prevented while allowing vertical movement thereof due to aradially projecting key 116 in elongated vertical key-way or slot 118 onone side of the plunger.

Aiiixed to the upper end of the screw shaft is a worm gear 119 meshingwith a worm 120 driven through connection 122 by a second stepping motor124, similar to motor 98. Actuation of motor 124 therefore rotates worm120, which rotates gear 119, which rotates screw shaft 112, whichvertically moves plunger 102 and the diamond contained therein to feedit toward wheel 20.

Both of these stepping motors 98 and 124 are electrically connected toswitch control mechanism (FIGS. 3 and 6). The switch mechanism isoperated manually and controls the stepping motors 98 and 124. It mayincorporate either one switch 140, a pair of switches and 142, or anyother number of switches to cause the desired number of actuations ofboth stepping motors per revolution of cam 144. Rotation of earn 144 ismanually achieved by a crank 146 mounted to the front of the switchhousing 148. Suitable spring detent means 150 interfits with grooves 152in a locator disc 153 mounted to the same shaft 154 as cam 144 and crank146. The crank may be rotated in small, exact arcuate amounts foraccuracy. For example, rotation of the crank one revolution or fourclicks first actuates switch 140 by depressing its cam follower rollerwhich closes the switch to actuate stepping motor 98 electricallyconnected to terminals and to simultaneously actuate stepping motor 124electrically connected to terminals 172. Then, the adjacent switch 142-is actuated by follower roller depressing the switch to again actuatestepping motor 98 through terminals 174 and stepping motor 124 throughterminals 176. Each switch actuates both stepping motors so thatrotation of manual crank 146 creates simultaneous feed of the dressingtool 106 towards the wheel, and lowering of the entire spindle assembly,i.e. wheel feed towards workpiece platform 16. There are two switches,and each actuates the stepping motors when shifted in either direction.Thereby the stepping motors are actuated four times per each crankrevolution. Presently, it is found that by causing tool feed and wheel'eed of 0.00005 inch each for each quadrant of crank turn, a total feedper revolution of 0.0002 inch occurs to give good results. This may bevaried. Since each switch actuates each feed system for the same timeperiod, and since the two feeds must be exactly the same, the motor anddrive means must be geared to provide the same linear feed.

7 Operation In the operation of the apparatus 10 illustrated in FIG. 1,the workpiece which is to have a predetermined amount (x) of materialremoved from its surface (FIG. 7) is placed and held upon bed 16 by anysuitable retention means. Next, grinding wheel 20 is placed intooperation by actuation of a suitable switch (not shown) to rotatespindle 68 through a belt and pulley mechanism or other suitableconventional drive connection (not shown). Before the grinding operationbegins, knob 114 with an indicator dial adjacent thereto may, ifnecessary, be unlocked from the interconnected gearing and rotated byhand to manually lower the diamond dressing tool 106 to a position nearthe surface of wheel 20. Then hydraulic control 110 is actuated to causethe hydraulic mechanism 103 to cause the dressing tool assembly and dirtbarrier slide plate 104 to reciprocate back and forth over the wheelsurface. Since the valving and hydraulic passageways, for thisreciprocation are not part of the inventive concept, are conventional,and would only lengthen this specification unduly, a detaileddescription is not here given. Then crank 146 is rotated a revolution ata time until it begins to contact the wheel while reciprocating. Crank146 is repeatedly rotated small amounts to take the desired number often thousandths from the wheel to dress it properly, and also toestablish an important tool reference point. The reciprocation of thediamond is then stopped at the position illustrated in FIG. 2 out of theway of the wheel. It is not vertically retracted from this position,however, since this would destroy its use as a reference for thecompensating mechanism. Next, the bed is actuated to start it toreciprocate and move the workpiece back and forth beneath the wheel.Then, manual crank 44 is rotated to drive worm 52 and thus gear 54affixed to screw shaft 56 to rotate screw shaft 56 and lower spindlehousing 58 as well as spindle 68 and wheel 20 until the wheel is insparking contact with workpiece 1%. Since the dressing tool is mountedto the spindle housing or housing portions connected thereto, it movesdirectly with the spindle housing and the wheel as the wheel is loweredand therefore remains in its reference position as illustrated in FIG. 2and as shown graphically in FIG. 7. It is then ready to grind theworkpiece. guard 19 limits the travel of hot particles during grinding.)Continued feed of the wheel may be manually using the wheel 44.Alternatively, it may be through an automatic (A conventional 6 toolacross the wheel to remove any desired amount (z) from the surface ofthe wheel. Any amount of material may be removed from the wheel toobtain proper dressing, i.e. to remove any irregularities on the surfaceof the wheel and/ or any particles embedded into the wheel. As

tool 106 is lowered the amount (z) to be dressed from the wheel, by itsrespective stepping motor 124, the entire spindle wheel will also besimultaneously lowered this same exact amount (z) by stepping motor 98and its cooperative screw drive mechanism. Therefore, it does not matterhow much of the Wheel is removed in dressing, since the wheel willalways be lowered a compensating amount toward the workpiece. Then thefinal pass is taken byreciprocating the workpiece under the wheel, withthe result that the wheel cuts exactly to line 191 to remove the exactamount (x) which was pre-set to be taken from its surface. This accurateresult occurs regardless of the hardness of the material of theworkpiece, or of the characteristics of the dressing wheel, or of theamount of wheel removed during dressing, or of the amount of wheel wearin previous passes. The important factors are the initial tool referencepoint achieved with the first dressing (FIG. 7) and the final dressingjust prior to the final pass or passes so that the automaticcompensation for the distance (y) (z) is made for the wheel as well asthe tool to obtain a removal of (x) thickness of stock. It has beenfound with repeated operation of the apparatus that it 7 workscompletely effectively, and extremely accurately,

incremental feeding mechanism using panel 42 and motor 50 with wheel 44servingto pre-set the total amount of stock to be removed. In eithercase, thethickness of stock which the machine theoretically removes isindicated on the wheel disc 15. As the wheel 20 is slowly loweredsuccessive amounts from the position illustrated in FIG. 7 to grind thesurface of workpiece 190, if the wheel had no wear (an impossiblecondition), at the end of the (x) amount of wheel feed, the lowersurface of the wheel should still be of a diameter represented byphantom line 20' in FIG. 8 and should have removed exactly (x) inches ofstock to be at line 191 on the workpiece. This was the thickness removedaccording to dial 45. However, the wheel surface has a definite amountof wear, for example, plus or minus 0.0001 inches in a cut of a fewthousandths of an inch. Thus, as shown by the exaggerated condition inFIG. 8, the actual surface of the wheel will be in line 193, a distanceof (y) inches above phantom line 1&1 where it should be at the bottom ofthe thickness (x). Thus, this (y) amount of wheel wear is exactly equalto the (y) thickness discrepancy of the stock removed, i.e. of actualsurface 193 above theoretical surface 191.

The novel apparatus, however, provides automatic compensation for thisin the following manner. Just prior to the final pass or passes of theworkpiece past wheel 20, the wheel is dressed with tool 106. This isachieved by rotating crank 146 to lower the tool 1% toward the wheel.There will be a gap (y) between the diamond tip of the dressing tool (inits reference position) and the upper surface of wheel 20, due to thewheel wear which has displaced the worn wheel surface from the originalsurface. Thus, as crank 146 is initially rotated to actuate switches 140and 142 and rotate stepping motor to drive worm 120 and worm gear-119around screw shaft 112, the tool will first have to move across distance(y) to con-tact the wheel. This is done in successive increments of0.00005 inch. It should be noted that switches 140 and 142simultaneously actuate stepping motor 98 also so that it rotates wormgear 90 in the same increments to simultaneously lower screw shaft '56.Exact amounts of feed of both the'spindle housing with wheel and thedressing tool occurs. Thus, as the diamond tip moves (y), the entireapparatus including the spindle housing, spindle, wheel and dressingtool moves the distance (y) toward the work Next, crank 146 is turned afurther amount to time after time, in an automatic manner, withoutrequiring any special operating skill or patience.

Certain advantages in addition to those cited above will occur to thosein the art upon studying the foregoing illustrated form of the inventionand the principles involved. Also, certain obvious modifications mayreadily occur to those in the art, upon studying the invention astaught, without departing from the inventive principles and concepts.These obvious modifications are deemed to be part of this invention,which is to be limited only by the 1 scope of the appended claims andthe reasonable equivalents to those defined therein.

We claim:

1. In a grinder, a workpiece support bed, .and support means for agrinding wheel and wheel dresser adjustable with respect to said bed;grinding feed means to feed said wheel and dresser toward said bed togrind a workpiece; means including a stepping motor to feed said dressertowards said wheel controlled increments; a second stepping motoroperably connected with said support means and independent of saidgrinding feed means to advance said grinding wheel and dresserindependently of said grinding feed means; and electrical switch meansoperably connected with both of said stepping motors to simultaneouslyactuate both said stepping motors; said I stepping motors and feed meansbeing arranged to cause equal feeds thereof and thereby enablecompensation of said wheel with dressing thereof, for wheel loss andwear.

2. A grinder comprising: a housing containing a rotatable spindle andgrinding wheel and adapted to be adjustably mounted to a support toenable said wheel to be moved toward or away from a workpiece on saidsupport for feeding the wheel into the workpiece; grinding feed drivemeans operably connected to said housing andsupport to effectuate saidfeed including operating means to operate said feed drive means;compensator motor means operably connected to said drive means andcapable of operating said drive means independently of said operatingmeans; a wheel dressing tool adjustably mounted on said housing adjacentsaid wheel, normally movingwith said housing, andv adapted to be fedtoward said wheel with respect to said housing; dresser drive means toeffectuate said dresser feed; dresser feed motor means operablyconnected to saiddresser feed drive means; actuator means independent ofsaid operating means operably associated with both said dresser motormeans to cause a pre-selected dresser feed, and said com- 1 pensatormotor means to cause simultaneous actuation of said motor means to movesaid housing, including said wheel and dresser means toward saidworkpiece an amount equal to the feed of said dressing tool towards saidwheel and thereby compensate for both wheel wear and wheel dressingloss.

3. A grinding wheel assembly, comprising: spindle and housing meanssupporting a grinding wheel, dressing tool means and work support means;motor operated adjustable support means for said dressing tool meansincluding a first stepping motor capable of moving said tool incrementalamounts with respect to said housing and toward said wheel; motoroperated adjustable support means for said spindle and housing includinga second stepping motor capable of moving said wheel and said tool meansincremental amounts toward said work support means; and progressiveelectrical switch actuating means operably associated with the motormeans of both said adjustable support means to cause simultaneouscompensating wheel and tool movement in exact increments toward saidwork supporting means with tool movement toward said wheel uponactuation of the dressing action.

4. A grinder comprising: support means for a workpiece, and a spindleand wheel housing movable towards said support means; grinding wheel andspindle means rotatably supported in said housing including means tofeed said wheel toward said support means; a wheel dresser supported onsaid housing adjacent said wheel and adapted to normally move with thehousing; said dresser being supported on dresser drive means adapted tomove it with respect to said housing so as to feed it toward and awayfrom said wheel; stepping motor means connected to said dresser drivemeans for incremental operation thereof; said spindle housing alsoincluding compensating drive means operably connected to a secondstepping motor for incremental drive thereof; said dresser drive meansand motor and said spindle housing compensating drive means and motoradapted when actuated to move the dresser towards said wheel an amountequal to the movement of the spindle housing, wheel, and dresser towardsaid workpiece support means; and switch means electrically connected tosaid stepping motors to actuate them simultaneously and momentarily tomove them an increment whereby wheel compensation is made for both wheelwear and dressing loss when the wheel is dressed.

5. A grinder, comprising: workpiece support means, and a spindle andwheel housing rotatably supporting a grinding wheel and spindle; screwdrive means to feed said wheel and spindle toward said support means;first feed motor means operably connected to said screw drive means; asecond, independent, compensating stepping motor means operablyconnected to said screwdrive means for incremental actuation thereof;wheel dresser means operably supported on said housing adjacent saidwheel and adapted to normally move with said housing and wheel; saiddresser having drive means between it and said housing and adapted tomove it with respect to said housing so as to feed it toward said wheel;a third, stepping motor means operably connected to said dresser drivemeans for incremental driving thereof; switch means electricallyconnected to both said second motor means and third motor means andadapted to actuate them substantially simultaneously; and saidcompensating motor means and screw drive means adapted to move saidwheel and dresser means toward said workpiece support means an amountequal to the movement of said dresser by said third motor means anddresser drive means toward said wheel to provide exact compensation ofsaid wheel when the wheel is dressed for both wheel wear and dressingloss.

6. A grinder, comprising: a support including a workpiece supporting bedand a spindle and wheel housing spaced from said bed and rotatablymounting a spindle and grinding wheel; said housing being adjustable onsaid support; a rotatable screw shaft between said support and housingand adapted to move said housing and wheel toward and away from said bedwhen rotated in opposite directions; a first electrical feed motor; aworm gear operated by said motor and engaged with a gear keyed to saidscrew shaft to enable said motor to rotate said shaft but to preventrotation of said shaft from another source of power operably engagedwith said shaft; a second electrical motor of the stepping type forincremental operation; a worm gear operated by said second motor andengaged with a gear collar threadahly engaged around said screw shaft toenable said second motor to rotate said collar for vertical drivingmovement of said shaft, but to prevent rotation of said collar, wormgear and second motor by rotation of said shaft from another source sothat rotation of said shaft from another source causes vertical movementof said shaft through said collar; a wheel dresser operably supported onsaid housing adjacent said wheel and adapted to normally move with saidhousing, wheel and spindle; a second screw shaft between said dresserand housing and adapted to drive said dresser toward and away from saidwheel; a third electrical motor, also of the stepping type forincremental operation, operably connected to said second screw shaft;and electrical switch means electrically con nected to both of saidstepping motors to simultaneousl operate them in increments of movementto shit-t said housing, wheel and dresser toward said bed, and shiftsaid dresser towards said wheel, equal predetermined incremental amountsto automatically compensate for wheel wear and loss.

References Cited by the Examiner UNITED STATES PATENTS 1,896,533 2/33Vuilleumier l25l1 X 2,545,730 3/51 Fouquet til-165.14 X 2,944,373 7/60Mentley et al. 51l65.l4 X

LESTER M. SWINGLE, Primary Examiner.

J. SPENCER OVERHOLSER, Examiner.

1. IN A GRINDER, A WORKPIECE SUPPORT BED, AND SUPPORT MEANS FOR AGRINDING WHEEL AND WHEEL DRESSER ADJUSTABLE WITH RESPECT TO SAID BED;GRINDING FEED MEANS TO FEED SAID WHEEL AND DRESSER TOWARD SAID BED TOGRIND A WORKPIECE; MEANS INCLUDING A STEPPING MOTOR TO FEED SAID DRESSERTOWARDS SAID WHEEL CONTROLLED INCREMENTS; A SECOND STEPPING MOTOROPERABLY CONNECTED WITH SAID SUPPORT MEANS AND INDEPENDENT OF SAIDGRINDING FEED MEANS TO ADVANCE SAID GRINDING WHEEL AND DRESSERINDEPENDENTLY OF SAID GRINDING FEED MEANS; AND ELECTRICAL SWITCH MEANSOPERABLY CONNECTED WITH BOTH OF SAID STEPPING MOTORS TO SIMULTANEOUSLYACTUATE BOTH SAID STEPPING MOTORS; SAID STEPPING MOTORS AND FEED MEANSBEING ARRANGED TO CAUSE EQUAL FEEDS THEREOF AND THEREBY ENABLECOMPENSATION OF SAID WHEEL WITH DRESSING THEREOF, FOR WHEEL LOSS ANDWEAR.